Saliva has a major influence on the acid/base and oxidative metabolisms of the mixed bacteria of saliva and dental plaque. The main objective of our research is to develop an understanding of how saliva and its nitrogenous components, particularly its peptides and proteins, regulate and modify the metabolism and growth of the mixed bacterial populations found in the human oral cavity. Sialin, an arginine peptide discovered earlier in our laboratory is mainly responsible for the pH-rise activity of saliva and may be an agent useful in the control of dental caries. Therefore, the metabolism of Sialin by the oral microflora will be studied using Sialin labelled with 14C using a variety of biochemical techniques. The effect of Sialin on various parameters of carbohydrate and urea metabolism by the mixed oral bacteria will be determined. The arginine polypeptides present in whole saliva will be tested as possible precursors of Sialin. Using similar techniques, the pH-rise activity of pure cultures of oral microorganisms will be examined. Other salivary peptides will be isolated, identified, and tested as oxidizable substrates for the mixed bacteria of saliva and dental plaque. Degradation of salivary proteins and polypeptides by the oral bacteria into small peptides and amino acids will be determined. Their effects on the acid/base and oxidative metabolisms of the mixed oral flora will be examined. The influence of pH, saliva, and salivary peptides on the microbial composition of the salivary and dental plaque microfloras will be examined in vitro.